Ν3 Vibrational Mode Research Articles

Vibrational state-specific nonadiabatic photodissociation dynamics of OCS+ via A2Π1/2 (ν1 0 ν3) states.

The identification and analysis of quantum state-specific effects can significantly deepen our understanding of detailed photodissociation dynamics. Here, we report an experimental investigation on the vibrational state-mediated photodissociation of the OCS+ cation via the A2Π1/2 (ν1 0 ν3) states by using the velocity map ion imaging technique over the photolysis wavelength range of 263-294nm. It was found that the electronically excited S+ product channel S+(2Du) + CO (X1Σ+) was significantly enhanced when the ν1 and ν3 vibrational modes were excited. Clear deviations in the branching ratios of the electronically excited S+ channel were observed when the vibrational modes ν1 and ν3 were selectively excited. The results reveal that vibrationally excited states play a vital role in influencing the nonadiabatic couplings in the photodissociation process.

Vibrational spectroscopy of shock compressed condensed phase nitrous oxide: Frequency shifts in the ν1 mode

Over many years, we have published vibrational spectra of molecular materials at extreme pressure and temperature obtained using shock compression and coherent Raman spectroscopy methods. For diatomic molecules, we were able to extract vibrational temperatures from the intensities of spectrally resolved vibrational hot bands. Larger molecules in the condensed phase suffer band broadening effects that obscure the vibrational hot bands as the anharmonicities are typically smaller than the widths of the bands. This inability to resolve the hot bands inhibits the extraction of vibrational temperature and the measurement of the vibrational frequency of the fundamental. Here, we use a hot band model based on gas-phase anharmonic coupling coefficients to fit coherent anti-Stokes Raman spectra of the ν1 vibrational mode of shock compressed condensed phase N2O with shock pressures and temperatures estimated from literature equations of state and compare to fits from a model using a single Gaussian peak. We report the resulting vibrational frequency shifts with shock pressure.

Carbon–sulfur chains: A high‐resolution infrared and quantum‐chemical study of C3S and SC7S

AbstractIn the course of a 5 μm high‐resolution infrared study of laser ablation products from carbon–sulfur targets, the ν1 vibrational mode region of linear C3S has been studied continuously from 2046 to 2065 cm−1. Besides the prominent vibrational fundamental, the region was found to feature the , and even hot bands, the latter two of which were observed for the first time. Owing to the high signal‐to‐noise ratio obtained, the ν1 mode of S could also be observed in natural abundance for the first time at high spectral resolution in the infrared. At 2061 cm−1, hidden inside the branch of the C3S ν1 fundamental mode, a weak new band is observed which exhibits very tight line spacing and stems from a heavy both carbon and sulfur containing carrier. On the basis of high‐level quantum‐chemical calculations of selected carbon–sulfur chains and other carbon‐rich cumulenes, this feature is attributed to the ν5 vibrational fundamental of linear SC7S, which stands for the first gas‐phase spectroscopic detection of this long cumulenic chain.

Study of the dependence of the photoacoustic signal amplitude from methane on different collisional partners

In a previous work we observed that the photoacoustic signal from methane in air decreases to one-seventh the figure obtained in mixtures with pure nitrogen. A close resonance between oxygen's first vibrational mode (ν) and the methane bending modes may be responsible for this phenomenon. Indeed, the long relaxation time of the ν mode (1554cm−1) causes the oxygen to store energy internally instead of releasing it to heat. In this work we study different collisional partners (Helium, C2Cl2F4) which may help transfer this vibrational energy to kinetic.In order to carry out the experiment we used the resonant photoacoustic technique by means of an OPO tuned at 3.3μm, which corresponds to the methane ν3 vibrational mode, and an aluminum acoustic resonator with rectangular cross section, Brewster windows at the resonance nodes of the second longitudinal mode at 2300Hz and Q-factor of 165. A rate-equation-based model, which describes the time evolution of the excited populations and the heating of the sample for the case of Helium, shows good agreement with the experimental results. The addition of C2Cl2F4 showed an increase of the methane PA signal up to values even higher than for methane-nitrogen mixtures.

A Vibrational Spectroscopic Study of the So-Called Healing Mineral Papagoite CaCuAlSi2O6(OH)3

ABSTRACT Papagoite is a silicate mineral named after an American Indian tribe and was used as a healing mineral. Papagoite CaCuAlSi2O6(OH)3 is a hydroxy mixed anion compound with both silicate and hydroxyl anions in the formula. The structural characterization of the mineral papagoite remains incomplete. Papagoite is a four-membered ring silicate with Cu2+ in square planar coordination. The intense sharp Raman band at 1053 cm−1 is assigned to the ν1 (A 1g) symmetric stretching vibration of the SiO4 units. The splitting of the ν3 vibrational mode offers support to the concept that the SiO4 tetrahedron in papagoite is strongly distorted. A very intense Raman band observed at 630 cm−1 with a shoulder at 644 cm−1 is assigned to the ν4 vibrational modes. Intense Raman bands at 419 and 460 cm−1 are attributed to the ν2 bending modes. Intense Raman bands at 3545 and 3573 cm−1 are assigned to the stretching vibrations of the OH units. Low-intensity Raman bands at 3368 and 3453 cm−1 are assigned to water stretching modes. It is suggested that the formula of papagoite is more likely to be CaCuAlSi2O6(OH)3 · xH2O. Hence, vibrational spectroscopy has been used to characterize the molecular structure of papagoite.

Phonon coupling of water monomers in a solid nitrogen matrix

The infrared absorption spectra of the H2O, HDO, and D2O monomers isolated in solid N2 have been recorded at various temperatures between 4 and 30 K. A study of the absorption features of the ν1, ν2, and ν3 vibrational modes for each monomer shows their optical line shapes to be strongly temperature dependent. For all three modes, a decrease in the absorption amplitude and a proportional broadening of the linewidth was observed with increasing temperature, while the integrated absorbance remained constant. These observations were explained in terms of phonon coupling, by which high frequency intramolecular modes decay by exciting matrix phonons. Fits of the linewidth for the lowest frequency ν2 vibrational mode to the predicted vibrational relaxation rate in a solid medium gave average phonon mode frequencies consistent with the Debye frequency for solid N2.

A study of electron interactions with silicon tetrafluoride: elastic scattering and vibrational excitation cross sections

We report absolute differential cross sections for elastic electron scattering from SiF4. The incident electron energy range is 1.5–200 eV, while the scattered electron angular range was from 15° to 150°. The absolute scale of the differential cross sections was set using the relative flow technique with helium as the reference species. Corresponding integral elastic and momentum transfer data have been derived from our differential measurements. As a part of this study, independent atom model calculations were also performed. Those computations were found to be in generally quite good accord with the experimental results at both the differential and integral levels. In addition, excitation function measurements at a scattering angle of 60° and in the energy range 1–14 eV for the ν3 (d-stretch) and ν4 (d-deformation) fundamental vibrational modes are reported. Finally, differential cross sections for all four fundamental modes (ν1, ν2, ν3, ν4) at the single electron energy of 7 eV are given. These vibrational excitation measurements, when coupled with the elastic angular distributions in the 5–8 eV energy range, demonstrate the presence of a t2-symmetry shape resonance.

Vibrational spectroscopy and solubility study of the mineral stringhamite CaCuSiO4·H2O

Stringhamite CaCuSiO4·H2O is a hydrated calcium copper silicate and is commonly known as a significant ‘healing’ mineral and is potentially a semi-precious jewel. Stringhamite is a neosilicate with Cu2+ in square planar coordination. Vibrational spectroscopy has been used to characterise the molecular structure of stringhamite.The intense sharp Raman band at 956cm−1 is assigned to the ν1 (A1g) symmetric stretching vibration. Raman bands at 980, 997, 1061cm−1 are assigned to the ν3 (A2u, B1g) antisymmetric stretching vibrations. Splitting of the ν3 vibrational mode supports the concept that the stringhamite SiO4 tetrahedron is strongly distorted. The intense bands at 505 and 519cm−1 and at 570cm−1 are assigned to the ν2 and ν4 vibrational modes.The question arises as to whether the mineral stringhamite can actually function as a healing mineral. An estimation of the solubility product at pH<5 shows that the cupric ion can be released. The copper ion is a very powerful antibiological agent and thus the mineral stringhamite may well function as a healing mineral.

Whelanite Ca5Cu2(OH)2CO3,Si6O17·4H2O—A vibrational spectroscopic study

Whelanite Ca5Cu2(OH)2CO3,Si6O17·4H2O is a hydrated hydroxy mixed anion compound with both silicate and carbonate anions in the formula. The structural characterisation of the mineral whelanite remains incomplete. Whelanite is probably a neosilicate with Cu2+ in square planar coordination.Two Raman bands at 1070 and 1094cm−1 are assigned to the ν1 symmetric stretching modes of the CO32− units. The observation of two symmetric stretching modes supports the concept of two non-equivalent CO32− units in the whelanite structure. The intense sharp Raman band at 1006cm−1 is assigned to the ν1 (A1g) symmetric stretching vibration of the Si6O17 units. The splitting of the ν3 vibrational mode offers support to the concept that the SiO4 tetrahedron in whelanite is strongly distorted. A very intense Raman band observed at 666cm−1 with a shoulder at 697cm−1 is assigned to the ν4 vibrational modes. Intense Raman bands at 3534, 3556, 3550 and 3595cm−1 are assigned to the stretching vibrations of the OH units. Low intensity Raman bands at 2910, 3187 and 3453cm−1 are assigned to water stretching modes. Thus, vibrational spectroscopy has been used to characterise the molecular structure of whelanite.Whelanite is a mineral that could be conceived as a healing mineral.

Oxygen in Ge:Sn

The effect of doping with tin on the ν3 vibrational mode of oxygen in Ge has been studied. The appearance of three new series of absorption lines besides the ν3 oxygen vibration spectra was found. The spectrum structure in each series of lines found is similar to the ν3 oxygen spectrum structure in Ge. But unlike the ν3 mode, the fine structure due to rotational-vibrational interaction of the ν3 and ν2 modes is not observed and the spectrum structure remains up to temperatures of 130 K. The found three sets of absorption lines are ascribed to the ν3 vibration of interstitial oxygen disturbed by tin atoms located in the nearest environment. The assumption has been made that no rotation of oxygen around a Ge-Ge bond for a Ge-O-Ge quasimolecule disturbed by a neighbour Sn atom occurs.

Direct observation of the vibrational energy redistribution in (CF3)2CCO molecules resonantly excited by femtosecond infrared laser radiation

The dynamics of multiphoton excitation of (CF3)2CCO molecules has been investigated under the condition of resonant action of femtosecond infrared laser radiation on the ν1 vibrational mode of the C=C=O bond. It has been shown that the mode-selective excitation of this vibration occurs up to the ν = 6 level. The kinetics of the subsequent intramolecular vibrational energy redistribution from the ν1 mode has been measured. A value of 5 ± 0.3 ps has been obtained for the characteristic time of this process.

Raman spectroscopic study of the sulfite‐bearing minerals scotlandite, hannebachite and orschallite: implications for the desulfation of soils

AbstractThe structures of the naturally occurring sulfite‐bearing minerals scotlandite, hannebachite and orschallite have been studied by Raman spectroscopy. Raman bands are observed for scotlandite PbSO3 at 935, 880, 622 and 474 cm−1 and are assigned to the (SO3)2−ν1(A1), ν3(E), ν2(A1) and ν4(E) vibrational modes, respectively. For hannebachite (CaSO3)2·H2O these bands are observed at 1005, 969 and 655 cm−1 with multiple bands for the ν4(E) mode at 444, 492 and 520 cm−1. The Raman spectrum of hannebachite is very different from that of the compound CaSO3·2H2O. It is proposed, on the basis of Raman spectroscopy, that in the mineral hannebachite, the sulfite anion bonds to Ca through the sulfur atom. The Raman spectrum of the mineral orschallite Ca3[SO4](SO3)2·12H2O is complex resulting from the overlap of sulfate and sulfite bands. Raman bands at 1005 cm−1, 1096 and 1215 cm−1 are assigned to the (SO4)2−ν1 symmetric and ν3 asymmetric stretching modes. The two Raman bands at 971 and 984 cm−1 are attributed to the (SO3)2−ν3(E) and ν1(A1) stretching vibrations. The formation of sulfite compounds in nature offers a potential mechanism for the removal of sulfates and sulfites from soils. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Raman Spectroscopic Investigation of CH4 and N2 Adsorption in Metal−Organic Frameworks

The adsorption behavior of CH4 and N2 (298 K, 30 bar) in a series of isoreticular metal−organic frameworks (IRMOFs) was investigated by Raman spectroscopy. For CH4, the ν1 vibrational mode shifted to lower frequency by 7.6, 8.4, 11.0, 10.3, and 10.1 cm-1 from 2917 cm-1 when adsorbed to IRMOF-1, -6, -8, -11, and -18, respectively. Along this same series, the adsorbed N2 stretch exhibited smaller shifts of 2.7, 3.1, 4.2, 4.1, and 3.7 cm-1. These shifts arise because of interactions within the framework pores, and not with the outer crystal surface. In all cases, Raman spectra at pressures up to 30 bar showed that saturation of the sorption sites does not occur. The observed shifts of the vibrational modes for each gas indicate different chemical environments within different IRMOFs, pointing to the important role the linkers play in the adsorption of gases.

Raman Spectroscopic Study of the Molybdate Mineral Szenicsite and Comparison with Other Paragenetically Related Molybdate Minerals

The molybdate‐bearing mineral szenicsite, Cu3(MoO4)(OH)4, has been studied by Raman and infrared spectroscopy. A comparison of the Raman spectra is made with those of the closely related molybdate‐bearing minerals, wulfenite, powellite, lindgrenite, and iriginite, which show common paragenesis. The Raman spectrum of szenicsite displays an intense, sharp band at 898 cm−1, attributed to the ν1 symmetric stretching vibration of the MoO4 units. The position of this particular band may be compared with the values of 871 cm−1 for wulfenite and scheelite and 879 cm−1 for powellite. Two Raman bands are observed at 827 and 801 cm−1 for szenicsite, which are assigned to the ν3(E g ) vibrational mode of the molybdate anion. The two MO4 ν2 modes are observed at 349 (B g ) and 308 cm−1 (A g ). The Raman band at 408 cm−1 for szenicsite is assigned to the ν4(E g ) band. The Raman spectra are assigned according to a factor group analysis and are related to the structure of the minerals. The various minerals mentioned have characteristically different Raman spectra.

Photoacoustic spectroscopy of formaldehyde with tunable laser radiation at the parts per billion level

Selective and sensitive detection of formaldehyde (CH2O) was achieved using a grazing-incidence optical parametric oscillator (GIOPO), pumped at high repetition rate, as a light source for photoacoustic spectroscopy. The photoacoustic spectrum of formaldehyde was measured in the range from 2785 to 2840 cm-1 and an absorption line at 2805.0 cm-1 was selected for detection. Concentrations down to 20 ppbv (parts per billion by volume) formaldehyde in nitrogen were recorded. The detection limit determined by background fluctuations was 3 ppbv (S/N=1) for 3 s lock-in time constant and 3 min acquisition time. The 2805.0 cm-1 absorption line of the ν1 vibrational mode was chosen because of the absence of interference with water and carbon-dioxide bands. This allowed the direct detection of formaldehyde in laboratory air without filtering.

Heme Distortion Modulated by Ligand-Protein Interactions in Inducible Nitric-oxide Synthase

The catalytic center of nitric-oxide synthase (NOS) consists of a thiolate-coordinated heme macrocycle, a tetrahydrobiopterin (H4B) cofactor, and an l-arginine (l-Arg)/N-hydroxyarginine substrate binding site. To determine how the interplay between the cofactor, the substrates, and the protein matrix housing the heme regulates the enzymatic activity of NOS, the CO-, NO-, and CN(-)-bound adducts of the oxygenase domain of the inducible isoform of NOS (iNOS(oxy)) were examined with resonance Raman spectroscopy. The Raman data of the CO-bound ferrous protein demonstrated that the presence of l-Arg causes the Fe-C-O moiety to adopt a bent structure because of an H-bonding interaction whereas H4B binding exerts no effect. Similar behavior was found in the CN(-)-bound ferric protein and in the nitric oxide (NO)-bound ferrous protein. In contrast, in the NO-bound ferric complexes, the addition of l-Arg alone does not affect the structural properties of the Fe-N-O moiety, but H4B binding forces it to adopt a bent structure, which is further enhanced by the subsequent addition of l-Arg. The differential interactions between the various heme ligands and the protein matrix in response to l-Arg and/or H4B binding is coupled to heme distortions, as reflected by the development of a variety of out-of-plane heme modes in the low frequency Raman spectra. The extent and symmetry of heme deformation modulated by ligand, substrate, and cofactor binding may provide important control over the catalytic and autoinhibitory properties of the enzyme.

Isotropic and anisotropic collision-induced light scattering by gaseous sulfur hexafluoride at the frequency region of the ν1 vibrational Raman line

Experimental binary isotropic and anisotropic Stokes spectra of the collision-induced light scattered by gaseous sulfur hexafluoride are measured at the frequency region of the ν1 vibrational Raman line. They are compared to theoretical intensities due to dipole–multipole interactions. Taking into account the results of a previous study on the interaction-induced intensities in the Rayleigh wings of gaseous sulfur hexafluoride, an experimental value of the derivative of the dipole–octopole polarizability associated with the ν1 vibrational mode is provided and compared to the result of a recent ab initio calculation.

Photodissociation of the methane–argon complex. I. Ab initio intermolecular potential depending on the methane vibrational coordinates

We calculated the intermolecular potential for the complex methane–Ar in which the methane is deformed along the ν1 and the ν3 vibrational normal modes. We present a fit of the potential energy surface as a function of the three argon coordinates and the four normal mode coordinates qν3x, qν3y, qν3z, and qν1. This potential is used in the following paper [J. Chem. Phys. 117, 7562 (2002)] dealing with the calculation of the lifetimes of the quasibound states of the dimer with the methane monomer in the vibrationally excited ν3 state.

Vibrational emissions of CO213 trapped in rare gas matrices: Kinetic model for the intramolecular relaxation

The ν3 vibrational mode of CO213, trapped in a rare gas matrix, is excited by a laser pulse near 2300 cm−1. Emission is then observed in the 16 μm region and assigned to three transitions: namely, 3ν21-2ν20, 3ν21-2ν22, and 2ν20-ν21, which are all observed in neon and for the two sites in argon. 3ν21-2ν22 is missing in krypton. In xenon the emission, much weaker and longer (ms range), cannot be frequency resolved and behaves like spontaneous emission. In the other cases, all the recorded signals exhibit the characteristics of vibrational stimulated emission (VSE). The temporal profile of VSE is different for the three transitions and highly depends on the matrix material (1–100 μs). The relative intensities of the different VSE transitions depend on the matrix and on the energy of the exciting pulse. These results are interpreted using a kinetic model which takes into account absorption, spontaneous and stimulated emission, and nonradiative transfers between the involved vibrational levels. The model provides numerical simulations of the emissions, which are adjusted to experimental features (time behavior and relative intensities). Orders of magnitude values are thus extracted for the transfer rates and compared to literature values.

Free radicals in superfluid liquid helium nanodroplets: A pyrolysis source for the production of propargyl radical

An effusive pyrolysis source is described for generating a continuous beam of radicals under conditions appropriate for the helium droplet pick-up method. Rotationally resolved spectra are reported for the ν1 vibrational mode of the propargyl radical in helium droplets at 3322.15 cm−1. Stark spectra are also recorded that allow for the first experimental determination of the permanent electric dipole moment of propargyl, namely, −0.150 and −0.148 D for ground and excited states, respectively, in good agreement with previously reported ab initio results of −0.14 D. The infrared spectrum of the ν1 mode of propargyl-bromide is also reported. The future application of these methods for the production of novel radical clusters is discussed.